- Add a WeakTable to the VM. This is used to remember the

runtime/vm/weak_table.cc

Index: runtime/vm/weak_table.cc
===================================================================
--- runtime/vm/weak_table.cc	(revision 0)
+++ runtime/vm/weak_table.cc	(revision 0)
@@ -0,0 +1,65 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "vm/weak_table.h"
+
+#include "platform/assert.h"
+#include "vm/raw_object.h"
+
+namespace dart {
+
+WeakTable* WeakTable::SetValue(RawObject* key, intptr_t val) {
+  intptr_t sz = size();
+  intptr_t idx = Hash(key) % sz;
+  intptr_t empty_idx = -1;
+  RawObject* obj = ObjectAt(idx);
+
+  while (obj != NULL) {
+    if (obj == key) {
+      SetValueAt(idx, val);
+      return this;
+    } else if ((empty_idx < 0) &&
+               (reinterpret_cast<intptr_t>(obj) == kDeletedEntry)) {
+      empty_idx = idx;  // Insert at this location if not found.
+    }
+    idx = (idx + 1) % sz;
+    obj = ObjectAt(idx);
+  }
+
+  if (empty_idx >= 0) {
+    // We will be reusing a slot below.
+    set_used(used() - 1);
+    idx = empty_idx;
+  }
+
+  if (used_ < limit()) {
+    ASSERT(!IsValidEntryAt(idx));
+    // Set the key and value.
+    SetObjectAt(idx, key);
+    SetValueAt(idx, val);
+    // Update the counts.
+    set_used(used() + 1);
+    set_count(count() + 1);
+    return this;
+  }
+
+  // Grow the table and add the hash value.
+  return Rehash()->SetValue(key, val);

[siva, 2013/06/27 22:11:33]

instead of first finding a slot to add and then realizing a rehash is needed,
rehashing and again finding a slot to add why not
trigger a rehash after adding an entry. That is you add the entry first and then
if (used >= limit() return Rehash();

[Ivan Posva, 2013/06/27 23:59:12]

Done.

+}
+
+
+WeakTable* WeakTable::Rehash() {
+  intptr_t sz = size();
+  WeakTable* result = NewFrom(this);
+
+  for (intptr_t i = 0; i < sz; i++) {
+    if (IsValidEntryAt(i)) {
+      WeakTable* temp = result->SetValue(ObjectAt(i), ValueAt(i));
+      ASSERT(temp == result);
+    }
+  }
+  return result;
+}
+
+}  // namespace dart